The present invention relates to packing devices of inflatable type used in boring techniques.
In effect, it is known that, in these techniques, obturating devices are called upon, within the framework of diverse applications, which are placed in position in the wellbores and which, at the required depth, are activated by employing inflation means.
Such obturating devices, usually called xe2x80x9cpackersxe2x80x9d, are constituted by cylindrical tubular elements whose outer wall is constituted by a sleeve made of elastomer which is maintained between two metallic rings allowing it to be connected to an upstream and possibly downstream bore pipe.
It is known that packers are intended essentially to perform two functions, namely a function of anchoring and a function of seal with the rocks adjacent the wellbore. To that end, after introduction of the packer in the wellbore to the desired level, the elastomer sleeve is inflated by an injection under pressure of a fluid such as, preferably, cement, or by mechanical compression.
One difficulty arises from the fact that a packer must withstand considerable loads, sometimes exceeding one hundred tons, so that the stresses, particualrly the shear stresses, which are exerted on the elastomer sleeve cause a deformation thereof which is detrimental, on the one hand, to the quality of its anchoring and, on the other hand, to its qualities of seal.
This difficulty is increased due to the fact that the packer must perform the afore-mentioned functions while it is located in a particularly hostile environment, in particular by reason of the aggressive nature of the fluids encountered and the high temperatures. The effects of the latter are felt all the more so as the packer is at a considerable depth, in zones where the temperatures may sometimes exceed values of the order of 150xc2x0 C. It will be understood that, under such conditions, the mechanical qualities of the elastomer constituting the inflatable sleeve of the packers are much lessened.
In order to reduce the phenomena of deformation of the packers under the effect of such stresses, it has been proposed to reinforce the elastomer by adding thereto a metallic reinforcement constituted for example by blades of metal which are arranged in its mass like scales. Such packers are, on the one hand, of high cost price and, on the other hand, do not completely overcome the drawbacks mentioned above.
Furthermore, it has been observed that the packers of the prior state of the art act like traps with respect to rare gases such as helium, with the result that they prove to be porous upon passage of the latter.
Finally, by reason of their outer lining of elastomer, the packers prove to be fragile and this outer lining is sometimes deteriorated during their descent into the wellbore, this further contributing to their subsequent lack of mechanical strength.
The present invention has for its object to overcome these various drawbacks by proposing a novel type of packer able, on the one hand, to withstand the hostile conditions of a wellbore as well as the considerable mechanical stresses which are exerted thereon after its anchoring. It also has for its object, by improving the quality of this anchoring particularly significantly, to simplify the boring technique, in particular by avoiding being obliged to make reductions of wellbore diameter.
The present invention thus has for its object a device for obturating a wellbore, of the so-called packer type, comprising a central tubular element covered by a deformable peripheral sleeve, inside which is injected a fluid under pressure so as to deform said sleeve and apply it on the walls of the wellbore, characterized in that the deformable sleeve is constituted by a metal.
This metal may preferably be constituted by an alloy based on cupronickel.
In one embodiment of the invention, the inner wall of the sleeve forms at least one annular chamber which extends over at least a part of the surface of the sleeve and which is in communication, by an orifice, with the interior of the packer, this chamber being filled, before injection of the fluid under pressure, with a material non-miscible in the wellbore fluid. This material will advantageously be constituted by a hardened cement which, Linder the effect of the pressure due to the injection of the cement in the packer will crack, thus creating porosities forming as many passages which will allow the fluid injected under pressure to be admitted into the annular chambers and thus exert on the walls of the metallic sleeves considerable efforts of pressure distributed over the whole surface of the sleeve and which will ensure deformation of the walls thereof.
This chamber may advantageously be constituted by a bore made in the metallic sleeve which will be inwardly limited by the outer wall of a tube fitted in the sleeve.
The device according to the invention for obturating a wellbore, or packer, is particularly advantageous with respect to the devices of the prior art, insofar as, particularly when the fluid under pressure injected into the packer is constituted by cement, the latter may form one piece with the different elements of the packer and in particular with the deformable sleeve, this improving the resistance of the latter to the different stresses exerted thereon and in particular the weight of the upstreamn tubing.